The present invention concerns apparatus for separating imiscible lighter and heavier liquids and, in particular, hydrocarbon liquids and the like from water. More particularly, the invention concerns a liquid-liquid separator for use in a body of water for separating and removing crude oil from waste water, and specifically, waste water discharged from an offshore drilling platform.
Waste water disposal caissons are available which remove oil from waste water through the use of an internal spillover wier located above the means water level of the body of water in which such caissons are arranged. These caissons, however, are susceptible to the potentially adverse effect of wave action; namely, that the oil/water interface level in the caissons might momentarily rise above the spillover wier and allow water to enter the oil chamber from which it is desired to pump only oil.
The present invention restricts the upward flow of liquids in the upper section of that type caisson such that even under storm conditions, the oil level is increased only slightly during a rise in the water level immediately surrounding the caisson. This oil level falls an equivalently small amount when the water level immediately surrounding the caisson falls. A surge plate is located in the upper section of the caisson. A small hole in the surge plate restricts upward flow of liquids caused by wave action yet does not restrict downward flow of the inlet liquids and solid particles, such as sand.
A further advantage of the surge plate concept is that since the oil spillover wier does not have to be elevated much above the expected high mean water level, a smaller oil layer will be formed in the upper section of the caisson reducing thereby the possibility that the lower level of the oil level i.e. the oil-water interface will fall below the water inlet terminus.